The present invention relates to an attenuator for use in filtering high-frequency waves propagated in a transmission line of a direct current or a low-frequency alternating current.
An attenuator for filtering high-frequency waves propagated in a transmission line of a direct current of a low-frequency alternating current is known. The attenuator is used in connecting with the transmission line. In FIG. 1, there is shown an enlarged view of a portion of an attenuator which comprises ferrite beads (bead-shaped ferrite sintered bodies) 1.sub.1, 1.sub.2, 1.sub.3 - - - 1.sub.n (n is an integer of from 20 to 500) having a conductor 2 passed through the same. The ferrite is a compound having the general formula of MFe.sub.2 O.sub.4, wherein M is a bivalent metal such as Mn, Ni, Co, Mg, Cu, Zn and Cd. In such an attenuator, the high attenuation (more than 50 dB) can be obtained in the frequency range of about 500 kHz to about 5 GHz, but the attenuation is low in fequencies of higher than 5 GHz.
There is, in the prior art, another attenuator devised by the same inventors as those of the present invention. In FIG. 2, there is shown an enlarged view of a portion of the attenuator which comprises a conductor 2 which is enclosed firmly within a mixture 3 comprising a powder of ferrimagnetic material dispersed in an organic high polymer. The ferrimagnetic material may be ferrite powder, and the organic high polymer may be synthetic rubber. In such attenuator, the high attenuation (more than 50 dB) can be obtained in the frequency range of about 50 MHz to about 50 GHz, but the attenuation is low in frequencies of lower than 50 MHz.
By the present invention, there is provided an attenuator which can give high attenuation of more than 50 dB in the wide frequency range of from about 500 kHz to about 50 GHz.